Reproducibility of 6-minute walking test in patients with COPD

Abstract

The reproducibility of the 6-min walking test (6MWT) needs to be more solidly studied. This study aimed to investigate the reproducibility of two 6MWTs performed on subsequent days in a large and representative sample of patients with chronic obstructive pulmonary disease (COPD), and to quantify the learning effect between the two tests, as well as its determinants.In a retrospective observational study, 1,514 patients with COPD performed two 6MWTs on subsequent days. Other measurements included body composition (dual X-ray absorptiometry), dyspnoea (Medical Research Council scale) and comorbidity (Charlson index).Although the 6MWT was reproducible (intraclass correlation coefficient50.93), patients walked farther in the second test (391 m, 95% CI 155-585 m versus 418 m, 95% CI 185-605 m; p,0.0001). On average, the second 6MWT increased by 27 m (or 7%), and 82% of patients improved in the second test. Determinants of improvement o42 m in the second test (upper limit of the clinically important change) were as follows: first 6MWT ,350 m, Charlson index ,2 and body mass index ,30 kg?m -2 (OR 2.49, 0.76 and 0.60, respectively).The 6MWT was statistically reproducible in a representative sample of patients with COPD. However, the vast majority of patients improved significantly in the second test by an average learning effect of 27 m.KEYWORDS: Chronic obstructive pulmonary disease, 6-min walking test, reproducibility of results C hronic obstructive pulmonary disease (COPD) is a systemic disease characterised by progressive airflow limitation, exercise intolerance and physical inactivity [1,2]. Although the degree of airflow obstruction is frequently used as a marker of disease severity, it does not adequately reflect extrapulmonary manifestations of COPD [3,4]. Some modalities of field tests are available to assess these patients' exercise capacity [4], which better reflect the extrapulmonary features of the disease.The 6-min walking test (6MWT) is a simple and inexpensive test that provides a global and integrated response of both physical (pulmonary and nonpulmonary factors) and psychological factors [5,6]. The 6MWT is used to assess functional exercise capacity before and after interventions [7,8] and as a predictor of morbidity and mortality in COPD [9].In general, the 6MWT is a reliable test in COPD patients but a learning effect has been suggested [10-15], i.e. patients achieving a considerably higher walked distance when a second test is performed. Indeed, there is controversy about the size of the learning effect, which may range from 2.6% to 22% [10,11,[16][17][18][19][20]. Moreover, the external validity of the previous studies is limited due to the pre-specified inclusion criteria [10,11,13,18]. Furthermore, researchers usually used statistical analysis that did not demonstrate trends and agreement between both 6MWTs, thereby compromising the internal validity of the results [10]. Additionally, the determinants of improvement in walking distance remain unknown. Considering the importance of the 6...

Reproducibility of Cadence-Free 6-Minute Step Test in Subjects with COPD

“…This indicates that, for this population, the test is reproducible with reproducibility values similar to those obtained using other clinical exercise tests, such as 6-min walk test, which presents an ICC of 0.88 -0.94, [20][21][22] and shuttle-walk test, which presents an ICC of 0.87. 23 Moreover, the error value for this comparison was acceptable, presenting a mean error of 5.7 steps and limits of agreement ranging from Ϫ7.1 to 18.6 steps.…”

“…This characteristic could be an advantage over the 6-min walk test, which requires at least one previous test and a recovery time between them, totaling a time expenditure of at least 50 min. 20 However, since the 6-min walk test has been largely used, and it has already been validated and related to morbidity/mortality in COPD subjects, we suggest that 6MST should substitute for the walk test only under certain circumstances. The 6MST should be used when there is not an adequate area in which to perform it or when the time is too short to allow a Values are expressed as mean Ϯ SD.…”

“…The expected ICC value used was consistent with the mean value of ICC found in 6 min walk test reproducibility studies: 0.88 -0.94. [20][21][22] …”

Lung-Heart Clinical Crosstalk in the Course of Copd Exacerbation

“…The findings are in agreement with Stevenson et al [26], indicating that the resolution of COPD exacerbation is related to increased values of operating lung volumes (FEV 1 , IC). Moreover, in our study we found that a relatively small, but significant improvement in RV%TLC (-4%) and FEV 1 (+200 mL) may be accompanied by major (+121 m) improvement in 6MWT result, which is much higher than generally accepted as clinically significant [27,28]. Another possible explanation for positive correlation of FEV 1 and exercise is the fact that significant improvement of FEV 1 is usually not observed in stable COPD.…”

“…The minimal oxygen saturation during 6MWT in our study was significantly higher after treatment, when compared with baseline values. These data are of importance as they indicate that increased exercise tolerance was due to respiratory improvement and not due to the doctor forcing the patient to march faster or due to the patient's learning potential [28]. As expected, IC has not revealed the degree of hyperinflation, whereas RV%TLC, as one of the most accurate methods of measuring hyperinflation, could reflect static hyperinflation changes [27,29].…”